1. Field of the Invention
This invention relates generally to the manufacture of semiconductor devices and more specifically to seasoning and conditioning a polishing pad to polish tungsten on semiconductor wafers.
2. Description of the Related Art
Some of today's semiconductors include tungsten structures. Some advantages of using tungsten in semiconductors is that tungsten exhibits excellent resistance to electromigration effects, hillock formation, and humidity-induced corrosion. One example of a tungsten structure used in a semiconductor is a multilevel interconnect or plug. Another example of a tungsten structure used in a semiconductor is a local interconnect.
Tungsten Chemical Mechanical Polishing (CMP) is becoming increasingly important in the manufacturing of semiconductors as a technology to replace the reactive ion etchback (RIE) of blanket tungsten on a semiconductor wafer surface to form tungsten plugs.
With Tungsten CMP, the tungsten on the wafer is polished with the use of a polishing pad. Some types of polishing pads used to polish tungsten on semiconductor wafers include the SUBA 500, the IC 1000, and the IC 1400 manufactured by RODEL, INC., of Delaware. The tungsten polishing rates of a pad depend upon a chemical reaction. For a new polishing pad that is recently installed on a polisher, the tungsten polishing rates are relatively low in comparison to a "used" polishing pad. A new polishing pad lacks the chemical seasoning of a used pad and consequently does not attain a suitable chemical reaction of a used pad. This chemical reaction aids in polishing tungsten on a semiconductor wafer. Consequently, it is often necessary to "break in" or season a new polishing pad for the new polishing pad to have tungsten polishing rates within a specified range.
One method for breaking in or seasoning a new polishing pad is to polish multiple dummy wafers having an outer layer including tungsten on the circuit side or front side of the wafer with the pad until the polishing rates are elevated within specifications. For example, one range of acceptable tungsten polishing rates is 4000 angstroms to 6000 angstroms per minute for a CMP tool type polisher such as the CMP-V or the AUIRIGA manufactured by SPEEDFAM. A disadvantage of seasoning a polishing pad with dummy wafers is the expense and time consumed in processing the several wafers that may be required to bring the tungsten polishing rates of a pad within acceptable levels.
What is needed is an improved way to season a pad for polishing tungsten.